1. Field of the Invention
The present invention relates to a system for optimally planning an Intensity Modulated Radiation Therapy system.
2. Description of the Prior Art
So-called Intensity Modulated Radiation Therapy (IMRT) systems are well known in the art [see U.S. Pat. Nos. 5,663,999; 6,142,925; 6,076,005; 6052,435; 6,038,283; 5,764,723; 5,701,897; 5,673,700; 5,669,387; 5,622,174, and xe2x80x9cIntensity Modulated Radiation Therapyxe2x80x94Complications,xe2x80x9d Advance for Administrators in Radiology, Radiology Technology Profile, July, 1996]. IMRT systems using Dynamic Multileaf Collimators (DMLC) entail rotation of the linear accelerator gantry in coordination with the opening and closing of the DMLC jaws. When delivering IMRT, at any desired combination of gentry angle and DMLC jaw position, it is necessary that the linear accelerator beams be properly gated to insure that radiation is only applied at the proper time and in the proper doses.
The field of radiation delivery has long relied upon dose delivery using either uniform fields or fields that are have a dose gradient in only one direction. These latter fields are commonly known as xe2x80x9cwedged fieldsxe2x80x9d. Intensity Modulated Radiation Therapy systems demand that treatment planners be provided with a tool that allows optimization dose distributions. Up until the present time such planning has been either extremely difficult to design when using routine planning techniques or else simply impossible. While one of the initial proposals of IMRT planning advocated a simple method of involving the packing of the planned target volume with spheres of dose, each having a unique intensity, this technique was never fully developed. Other techniques based upon back projections and iterative optimization techniques have been advanced and commercialized. Although these techniques have been applied to routine radiation therapy targets and even to some radiosurgery targets they have yet to produce the highly conformal dose distributions with high dose gradients that are the hallmark of a good radiosurgery treatment plan.
The inventors have been active in the field of radiosurgery for approximately 15 years. During this time approximately 1800 radiosurgery patients have been treated thereby. This has provided the inventors with extensive experience in the planning and optimization of radiosurgery dose distributions. In order to assist those who are new to the treatment technique of developing high quality radiosurgery treatment plans, i.e. radiation dose distributions that are 1) highly conformal and 2) have exceedingly high dose gradients, the present invention provides a rule based system for dose planning. The system of the invention allows the clinician to use routine target outline techniques to define the 3D target volume and then the new computer code provides the location and intensity of the various xe2x80x9cisocentersxe2x80x9d used to xe2x80x9cpack the 3D volumexe2x80x9d.